In the field of solid fuel combustion, especially in the field of coal combustion, dust in the coal is difficult to be cleaned, which may limit the application of coal. In some furnaces which have strict requirements to the cleanness of the fuel, only expensive liquid fuel or gas fuel can be used.
Chinese patent application number CN 200620012646.2, titled “Clean burner using coal instead of oil”, discloses a method for use in clean combustion of coal and liquid dislagging. In the method for separating out molten dust in high temperature gas as disclosed, the air driven by an air damper sprays into the cylindrical chamber of the furnace along a direction tangent to the cylindrical furnace chamber and generates a centrifugal rotary force, so that the molten dust is separated from the high temperature gas and adheres to a sidewall around the furnace chamber before the molten dust is drained out. Although most of the coal dust can be separated out from the high temperature gas, the method disclosed in CN 200620012646.2 still cannot desirably separate the coal dust in the high temperature due to the following reasons.
(1) The air flow introduced into the furnace chamber must be corresponding to the fuel quantity added into the furnace chamber. Therefore, the number of air dampers disposed on the sidewall around the cylindrical furnace chamber is limited.
(2) The air flowing into the furnace chamber must be quickly mixed with the coal powder added into the furnace chamber for complete combustion. Therefore, the air dampers must be arranged adjacent to the location where the coal powder is added into the furnace chamber. The air dampers cannot be disposed freely along the length direction of the cylindrical furnace chamber.
(3) When the cylindrical furnace chamber is required to extend to improve the separation efficiency of the molten dust, the air damper cannot be disposed freely along the length direction of the cylindrical furnace chamber. Therefore, in the extended portion of the cylindrical furnace chamber, rotary force applied to the high temperature gas is not enough, and the separation efficiency of the molten dust is not high enough, e.g. 50-80%.
(4) When the cylindrical furnace chamber is extended to improve separation efficiency of the molten dust, the heat dissipating surface of the outer sidewall around the furnace chamber increases, which will lead to fall of temperature in the furnace and the coal dust in the furnace solidifies and cannot be separated in molten state.
Due to the disadvantages as previously discussed, clean combustion of coal is still a problem in coal combustion. In some industries which have strict requirements to the cleanliness of the fuel, e.g. ceramic industry and glass industry, the separation efficiency of the coal dust is only about 50-80%, which cannot meet the requirement of actual use. The separation efficiency must reach more than 95%, or even more than 99.5%. Therefore, at present, only fuel of high cleanliness, such as fuel oil, natural gas or petroleum coke having little ash, can be used. Cheap coal available in the market cannot be used to reduce cost.
In coal fired power generation field, coal powder cyclone furnace is an advanced combustion device. The cyclone furnaces uses the combustion air from the air intake device to centrifugally rotate the high temperature gas generated in combustion of the coal powder in the cyclone furnace to separate out the molten coal dust in the high temperature gas. However, the separation efficiency of the molten coal dust is desirable, e.g. about 50-70%, which causes the coal dust to adhere to the sidewall of the furnace and affects heat transfer. Therefore, it is very difficult to efficiently separate out molten dust in the fuel gas of the cyclone furnace in power industry.
In solid fuel gasification, solid material heating and melting, glass smelting or metallurgy industry involving high temperature chemical reaction, there is still no effective method and equipment which can separate out molten dust in the high temperature gas efficiently. Therefore, at present, to avoid generating a large amount of molten dust in high temperature gas, the following methods are used.
(1) Reducing the temperature of high temperature chemical reaction, so as to avoid generating a large amount of molten dust in high temperature gas.
(2) When a large amount of molten dust is generated in high temperature gas, feeding low temperature gas to quickly cool the high temperature gas, so that the molten dust in the high temperature gas condenses to solid.
(3) Using clean fuel, such as fuel oil or natural gas.
(4) Adding large size particles of the material to be melted in high temperature gas, so as to prevent the powder material from dispersing into the high temperature gas and melting.
(5) Using electric arc furnace to heat material directly, instead of using high temperature gas.
However, the methods as discussed previously inevitably reduces productivity and energy utilization efficiency and increase cost of production.
In solid fuel gasification, especially in coal gasification, fixed bed gas producer is generally used. The dust in the coal is needed to be removed in solid state, which requires the gasification temperature lower than the melting temperature of the dust in the coal, such as 1100-1250° C. The gasification efficiency of the coal in low temperature is low. The heat value of the coal gas is not high enough. The coal gas also contains a large amount of tar which may pollute the environment. Additionally, the coal used for gasification is relatively expensive.
As to natural gas made from coal, Chinese patent application number CN 200610075185.8, titled “Natural gas or hydrogen gas made from coal”, discloses a method for separating out coal dust, in which high temperature inflammable gas containing molten coal dust is mixed with cool inflammable gas. Rapid cool causes the molten coal dust to solidify to be collected via a cyclone collector. However, the method as disclosed in CN 200610075185.8 cannot collect the heat in the high temperature inflammable gas, and a complex process is needed to produce the high temperature vapor used for coal gasification. Additionally, the heat transfer efficiency is less than 80%.
In industrial furnace used in glass, steel rolling and metallurgy, high cleanliness fuel, for instance fuel oil or natural gas, is required. However, the temperature of the fuel gas from the industrial furnace is very high. If a regenerative heat exchanger can be used to recycle the residual heat in the gas for heating the oxygen containing gas to a high temperature, the heated oxygen containing gas can acts as the gasification agent of the coal powder. The residual heat in the gas of the industrial furnace can be effectively utilized, which facilitates generation of fuel gas at a temperature higher than the melting point of the coal dust and improves the heat transfer efficiency of the coal gas. Therefore, instead of using fuel oil or natural gas, coal powder can also be used in these furnaces, to reduce the cost of production. However, at present, there is no effective device to separate out molten dust in high temperature gas. Therefore, using fuel gas of industrial furnace to heat oxygen containing gas and gasify the coal powder to generate coal gas still cannot be realized.
In glass production, glass tank furnace which uses regenerative heat exchanger to collect the residual heat in the fuel gas has desirable heat efficiency. In glass tank furnace, glass batch floating on the liquid glass is heated by radiative heat transfer from the fire and melts. In fact, the glass raw material only absorbs about 25-30% of the heat generated by combustion of the fuel. The rest 70-75% of the heat is dissipated via the furnace surface or is taken away by the fuel gas. If the glass batch is sprayed into the high temperature gas in the form of powder, the glass batch will melt quickly because the powder material has high specific surface area and desirable heat transfer efficiency. Therefore, glass tank furnace smaller than conventional glass tank furnace is adequate to melt the glass batch of the same weight, which not only reduces surface heat dissipation of the glass tank furnace, but also reduces fuel gas generated. However, the glass batch is sprayed into the high temperature gas in the form of powder. The high temperature gas contains a large amount of molten glass dust. What is needed is, therefore, a device which can efficiently separate out the molten glass batch in the high temperature gas. The heat in the high temperature gas can be recycled via a dividing wall type heat exchanger or a regenerative heat exchanger, so as to remarkably reduce energy consumption in glass production.
In metallurgical chemistry, such as being disclosed in chapter III of Metallurgical Engineering Design published in June, 2006 by Chinese Metallurgical Industry Press, flash smelting furnaces are widely used due to high heat efficiency. However, the large amount of dust content in the gas may block the funnel uptake and the heat recovery boiler. If a device which can efficiently separate out molten dust in high temperature gas is provided, the cleaned high temperature gas can be conveyed to the heat exchanger for recycling the heat which can be used to heat the oxygen containing gas in the flash melting furnace, so as to recycle the residual heat in the high temperature gas and improve environment.
In metallurgy chemistry, especially in iron making industry, blast furnaces are widely used. In blast furnace iron making process, granular or bulk iron ore and hard coke are added into the blast furnace for mixing. In the blast furnace, the iron ore is reduced into iron in high temperature reductive circumstances. The granular or bulk iron ore has small specific surface area, the heat transfer and iron reduction reaction is very slow, which may lead to consumption of a large amount of hard coke and heat energy. If a method for separating out molten dust in high temperature gas is provided, the powder iron ore can be dispersed in the high temperature reductive gas. The powder iron ore has big specific surface area and high reduction and heat transfer efficiency. The powder iron ore is melted and reduced to liquid iron and molten slag in the reductive gas quickly. The liquid iron and the molten slag can be recycled via equipment which can be used to separate the liquid iron and the molten slag in the high temperature gas. A heat exchanger is used to recycle the heat in high temperature gas to heat oxygen containing gas. The high temperature oxygen containing gas incompletely burns with the coal powder and generates high temperature reductive gas. In this regard, no hard coke or little hard coke is used.
In refractory material production, electric arc furnace is used to directly heat the refractory raw material, to melt electric smelting zirconia corundum brick, which consumes a large amount of electric energy and leads to high cost of production.
Additionally, in high temperature chemical reaction, heat exchangers are widely used to efficiently utilize the residual heat of the high temperature gas. However, the high temperature gas in the heat exchanger is needed to be very clean and cannot contain a large amount of molten dust. Otherwise, the heat exchanger may be blocked quickly and cannot function properly. At present, there is no equipment available which can efficiently separate out molten dust in the high temperature gas and, therefore, heat in the high temperature gas containing a large amount of molten dust cannot be recycled by the heat exchanger.
In view of the foregoing, what is need, therefore, is to provide a method and equipment which can efficiently separate out molten dust in high temperature gas, so as to improve productivity, save energy and improve environment.